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Make reading the write_overlay more efficient. Instead of always reading the

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original file and then overwriting it with what we have in memory, just linearly
fill the buffer, closing gaps between our buffers with original file content as
needed.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@30927 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Michael Lotz 2009-05-30 17:21:10 +00:00
parent bc72ab054b
commit f06f5d708c
1 changed files with 54 additions and 37 deletions
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91
src/add-ons/kernel/file_systems/layers/write_overlay/write_overlay.cpp
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@ -451,54 +451,71 @@ status_t
OverlayInode::Read(void *_cookie, off_t position, void *buffer, size_t *length,
bool readPages)
{
if (position >= fStat.st_size) {
*length = 0;
return B_OK;
}
uint8 *pointer = (uint8 *)buffer;
write_buffer *element = fWriteBuffers;
size_t bytesLeft = MIN(fStat.st_size - position, *length);
*length = bytesLeft;
if (position < fOriginalNodeLength) {
void *superCookie = NULL;
if (_cookie != NULL)
superCookie = ((open_cookie *)_cookie)->super_cookie;
void *superCookie = NULL;
if (!fIsVirtual && _cookie != NULL)
superCookie = ((open_cookie *)_cookie)->super_cookie;
size_t readLength = MIN(fOriginalNodeLength - position, *length);
status_t result = B_ERROR;
if (readPages) {
iovec vector;
vector.iov_base = buffer;
vector.iov_len = readLength;
result = fSuperVnode.ops->read_pages(SuperVolume(),
&fSuperVnode, superCookie, position, &vector, 1, &readLength);
} else {
result = fSuperVnode.ops->read(SuperVolume(), &fSuperVnode,
superCookie, position, buffer, &readLength);
while (bytesLeft > 0) {
size_t gapSize = bytesLeft;
if (element != NULL) {
gapSize = MIN(bytesLeft, element->position > position ?
element->position - position : 0);
}
if (result != B_OK)
return result;
if (gapSize > 0 && !fIsVirtual && position < fOriginalNodeLength) {
// there's a part missing between the read position and our
// next position, fill the gap with original file content
size_t readLength = MIN(fOriginalNodeLength - position, gapSize);
status_t result = B_ERROR;
if (readPages) {
iovec vector;
vector.iov_base = pointer;
vector.iov_len = readLength;
if (readLength < *length)
memset((uint8 *)buffer + readLength, 0, *length - readLength);
} else
memset(buffer, 0, *length);
result = fSuperVnode.ops->read_pages(SuperVolume(),
&fSuperVnode, superCookie, position, &vector, 1,
&readLength);
} else {
result = fSuperVnode.ops->read(SuperVolume(), &fSuperVnode,
superCookie, position, pointer, &readLength);
}
// overlay the read with whatever chunks we have written
write_buffer *element = fWriteBuffers;
*length = MIN(fStat.st_size - position, *length);
off_t end = position + *length;
while (element) {
if (element->position > end)
if (result != B_OK)
return result;
pointer += readLength;
position += readLength;
bytesLeft -= readLength;
gapSize -= readLength;
}
if (gapSize > 0) {
// there's a gap before our next position which we cannot
// fill with original file content, zero it out
memset(pointer, 0, gapSize);
bytesLeft -= gapSize;
position += gapSize;
pointer += gapSize;
}
// we've reached the end
if (bytesLeft == 0 || element == NULL)
break;
off_t elementEnd = element->position + element->length;
if (elementEnd > position) {
off_t copyPosition = MAX(position, element->position);
size_t copyLength = MIN(elementEnd - position, *length);
memcpy((uint8 *)buffer + (copyPosition - position),
element->buffer + (copyPosition - element->position),
size_t copyLength = MIN(elementEnd - position, bytesLeft);
memcpy(pointer, element->buffer + (position - element->position),
copyLength);
bytesLeft -= copyLength;
position += copyLength;
pointer += copyLength;
}
element = element->next;